1. Field of the Invention
The present invention relates to an image reader and a copier. More particularly, the invention relates to a technique for inhibiting the unauthorized copy of a document of which the unauthorized copying is inhibited when the document image is read.
2. Description of the Related Art
Recently, the image forming apparatus having a copying function, such as a personal computer, printer and copying machine, is in wide spread. Accordingly, it is very easy to copy documents. In this circumstance, even a copyrighted document or a document with the unauthorized copy prohibition mark, such as “copy inhibition”, “copy forbidden” or “confidential” (those documents will be referred to as “confidential documents”) is easily copied. There is an original document, called “confidential document”, of the type which contains character strings, graphics, tables, graphs, etc., and important information to be prevented from being leaked. Recently, this type of document is copied in an unauthorized manner, and the important information (confidential content) of the document is leaked. This information leakage becomes problematic. Accordingly, the image forming apparatus with the copying function must be given the function to prohibit the fraudulent copy of the confidential document.
To prohibit voluntary and arbitrary copying operations of confidential documents or to permit the copying operations within fixed limits, various techniques have been proposed. Those techniques may be classified into the following techniques. A first technique is that the confidential document may be copied, but the quality of the resultant copy is extremely poor. A second technique is that the confidential document is printed on a copy/forgery protect sheet. In a third technique, a pattern image hard to see by the human eye or a copy prohibition mark, e.g., “copy prohibition”, is printed in a copy prohibiting area. The pattern or mark is registered in advance. When the document is read, the mark is detected, and the detected one is compared with the registered mark or pattern. When those are coincident with each other, the copying operation is controlled.
A conventional art for the control of the illicit copying of the confidential document is disclosed in Japanese Patent Laid-Open No. 231384/1995. In the publication, a pattern image having a function equivalent to that of the copy/forgery protect sheet is generated by the image processing technique. The copy/forgery protect sheet is a sheet having a special pattern image previously printed thereon. The special pattern is hard to see by the human eye, but it comes forth into view on the sheet when it is copied by the copying machine. When a document printed on the copy/forgery protect sheet is copied by the copying machine, warning characters, e.g., “copy inhibition”, appears on the copied sheet. As a result, psychological deterrent acts on the illicit copying act, and one can distinguish between the original and the copied sheet.
In the Japanese Patent Laid-Open No. 231384/1995, the warning character part and the background part, which is dither processed at a specific common density, are superinterposed, whereby a pattern image, which produces an effect equivalent to that by an anticopy/counterfeit sheet, is composed with the input image data, whereby the effect equivalent to that by the copy/forgery preventing sheet is produced using a normal sheet.
In this technique, when it is copied by using the copying machine, the warning characters emerges on the background of the copied sheet. Accordingly, the illicit copying act is psychologically deterred. However, the illicit copying act preventing technique cannot inhibit the copying act per se. In this sense, the technique fails to prevent the illicit copy.
A technique to solve this problem is proposed. In the technique, copy inhibition information is embedded in advance in the confidential document. The copying machine detects the copy inhibition information from the image as read, and controls the copying operation in accordance with the read information. The technique is disclosed in Japanese Patent Laid-Open Nos. 2000-76458, 2001-189855, 2001-346032 or others.
In Japanese Patent Laid-Open No. 2000-76458, there is disclosed a technique in which the copying machine recognizes a specific symbol attached to a copy-inhibited document. In other words, the copying machine is given the function of recognizing the specific symbol, thereby inhibiting the illicitly copying of the copy-inhibited document.
In Japanese Patent Laid-Open No. 2001-189855, copy inhibition information and/or information to permit the user to copy if special conditions are satisfied are embedded in a document to be printed out by using the bar code or electronic watermark technique. The copying operation is controlled in accordance with those pieces of information detected.
In Japanese Patent Laid-Open No. 2001-346032, two-dimensional codes are embedded in the background of the copy/forgery protect sheet. In this technique, the copy inhibition information may be contained in the two-dimensional codes of the background. The copying machine is given the function of detect the two-dimensional information. If the copy inhibition information is contained in the two-dimensional codes, the copying operation is stopped. In this way, it is possible to prevent information of the confidential document from being leaked by the illicit copying.
The conventional techniques involve the following problems, however. The technique of judging as to if the copying operation is to be stopped upon the recognition of the specific symbol as disclosed in Japanese Patent Laid-Open No. 2000-76458, cannot perform such high level copying operation controls as to permit a specific user to copy for each document, and to permit the user to copy the document after predetermined date and time are past.
In the technique of embedding copy inhibition information by using the electronic watermark technique as disclosed in Japanese Patent Laid-Open No. 2001-189855, the electronic watermark easily becomes unrecognizable through the copy generation (copying repeated a plurality of times). In other words, the watermark is easily deleted by the hard copying operation. Accordingly, the information embedded by the electronic watermark technique disappears. As a result, it becomes unknown whether or not the document is the confidential document.
Any of the publications mentioned above can deter the user from illicitly copying the confidential document, but cannot prevent the illicit copying act completely. To ensure the prevention of the illicit copying, the copying machine must be given the function to recognize that an object to be copied put on the machine is a confidential document of which the copying is inhibited, and to control the copying operation. The function of detecting the copy inhibition mark, bar code and the like may be realized by a relatively simple technique. Accordingly, it is not difficult to incorporate this function to all the copying machines.
To realize the function of detecting the electronic watermark, however, it is necessary to use relatively large scale process and high level technique. The realizing of its function is costly. Specifically, the following processes must be used: skew correction process, code data positioning process, process to detect a dot pattern embedded as a latent image in the image (electronic watermark detecting process), error correction process for increasing the judgement accuracy, and the like. For this reason, the current actual circumstance is that most of the machines are not provided with the electronic watermark detecting function. This tendency is found also in the case of the two-dimensional code. In this circumstance, also when the confidential document is copied by the copying machine not having the function to detect the two-dimensional code or the electronic watermark, the information as embedded in the form of the two-dimensional code or the electronic watermark disappears. As a result, even the fact that the document is the confidential document becomes unknown.
In the techniques of Japanese Patent Laid-Open No. 2000-76458 or Nos. 2001-189855 and 2001-346032, copy inhibition information is embedded in the form of the special symbol, or the bar code or two-dimensional code. And, the copy inhibition information is located on the white background part in a state that it is visible to the human eye. Accordingly, the user can clearly see a place of the copy inhibition information in the document. When a user with malice easily removes (hides, paints out, cuts out) the part of the document containing such copy inhibition information as bar code embedded therein, the document is printed out without stopping the copying operation. It is impossible to prevent the secret information from being leaked outside. In this case, the special symbol or the bar code which is indicative of the confidential document is invalid for the copying machine. This results in that security protection depends only on the morals of the user.
In the techniques of Japanese Patent Laid-Open Nos. 2001-189855 and 2001-346032, judgement as to if the copying operation is to be stopped or permitted is not made till the electronic watermark or bar code embedded in the document. High level detection/judgement process, such as the skew correction process, is required for the detection of the electronic watermark or bar code, as described above. Accordingly, long processing time is consumed, and an efficiency of copy reproduction is lowered.